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Water-compatible adhesive polymers have numerous applications in the biomedical field, including the joining of tissues to endogenous and exogenous materials. Biocompatible adhesive polymers find use in dental onlay adhesives and composites, bone cements, sealing of skin lacerations, wound dressing materials, attachment of engineered tissues, and attachment of medical device implants to tissues. Ideally, such adhesives should be non-immunogenic, biodegradable, and form innocuous degradation products. In situ activation of adhesive properties and rapid curing are also beneficial.
One strategy for improving the bioadhesive properties of polymers in aqueous environments is to introduce chemical groups which are known to possess such adhesive properties in nature. Mussel adhesive proteins are exceptional underwater adhesive materials which form tenacious bonds allowing for the anchoring of mussels to the substrates on which they reside. The amino acid 3-(3,4-dihydroxyphenyl)-L-alanine (DOPA) is a structural feature of mussel adhesive proteins and is thought to be responsible for both adhesion and cross-linking characteristics of mussel adhesive proteins. In particular, oxidation of DOPA to DOPA-quinone may lead to cross-linking of the mussel adhesive protein, while the dihydroxyphenyl form of DOPA is believed to be responsible for adhesion to substrates. However, simple introduction of DOPA or DOPA-like moieties into existing polymer architectures does not necessarily provide usable bioadhesives. For example, such groups may be prone to oxidation by air during storage, resulting in pre-mature (i.e., prior to use) cross-linking, and thus poor adhesion. Additionally, DOPA and DOPA-like moieties are prone to degradation by UV light.